This invention relates to a classifier for classifying powdery material in gas according to their particle size and specific gravity.
FIG. 3 shows a prior art classifier of this type. It has a cylindrical casing 1 provided at the upper part thereof with an inlet port 2 for the material to be classified which extends in a tangential direction with respect to the inner wall of the casing. Material-air mixture a is fed into the casing 1 through the inlet port 2 casing. Coarse particles are classified by the cyclone casing. Coarse particles are classified by the cyclone effect due to the vortex.
An externally driven vane wheel 3 is mounted in the upper part of the casing 1. It serves to blow off any unclassified coarse particles going toward an outlet port 7 by imparting a centrifugal force thereto, thereby separating any fine particles. Thus it serves to improve the classifying effect. The material-air mixture thus classified flows out of the casing through the outlet port 7 and is collected in a collector (not shown) such as a bag filter.
A gas (air) inlet port 4 is formed in the lower part of the casing 1. Air b fed into the casing 1 through the inlet port 4 forms an upward vortex by spinning vanes 5 (see FIG. 2d). The upward air current b separates any fine particles from the coarse particles and flows out through the outlet port 7 together with the separated fine particles.
The coarse particles c thus classified are discharged through a discharge port 6 formed in the bottom of the casing 1.
The vane wheel 3 comprises an inverted conical member 3a at its bottom, a disc 3b formed with a through hole and a plurality of vanes 3c provided between the conical member 3a and the disc 3b and arranged at equal angular intervals from one another.
In this type of apparatus, since the inlet port 2 and the vane wheel 3 are located on the same level as is apparent from FIG. 3, the material-air mixture a tends to reach the vane wheel 3 without sufficiently undergoing the cyclone effect. Thus, the density of the material-air mixture a is high, i.e. the air contains large amounts of coarse particles when it reaches the vane wheel 3. As a result, the vane wheel 3 suffers from a large load and gets worn rather severely. Also, the higher the density of the mixture, the lower the accuracy of classification and the more easily the coarse particles flow out through the outlet port 7.